1. Field of the Invention
The present invention, in general relates to both a method and apparatus for three-dimensional surface profile measurement systems and, more particularly, to multi-color imaging systems.
Three-dimensional (hereinafter also referred to as either "3D" or "3-D") imaging systems are known. In general, the purpose is to determine the shape of an object in three dimensions so that it can be either better understood, or if appropriate, reproduced. Ideally, the absolute value (dimensions) of the object are obtained as well. Such types of systems fall into two basic categories which are: 1) Optical Systems and 2) Surface Contact Systems.
Surface Contact Systems rely upon a stylus probe that uses a mechanical contact tip to probe the surface of an object. The information about variations in the depth of the contact tip of the probe at any given point along the surface of an object directly correlate to the depth of the object. Height and width data is determined merely by the position of the contact tip along an "x" and "y" axis. This information is then "digitized" for use in computer based systems or by numerically-controlled machines, as are well known in the respective arts.
Surface Contact Systems involve very slow and tedious manual operation for the probe to traverse an object. The ability to resolve detail is dependent upon the density (number of) scan passes made of an object. The more detail desired, the slower the process. Also the size of the contact tip of the probe precludes access from minute areas of the object, thereby providing inaccurate results.
Also, there are objects which are of a fragile nature, such as a butterfly for example, that precludes the making of any actual physical contact by a probe tip with the object. Also, contact based systems are not suitable for use with moving objects. Furthermore, the digitization of live objects, such as a person, cannot be easily accomplished with such systems because of the discomfort and innate resistance associated with standing still for protracted periods of time and also the discomfort arising from contact with a probe tip. Clearly, the applications and utility of such systems are limited.
Optical systems, in general, acquire a plurality of images of an object which are taken by various means. These images contain reflected patterns of light energy that are compared and processed by various known mathematical algorithms to obtain data relating to the three dimensions of the object. Often, calibration with an object of known dimensions precedes the use of such types of systems if the absolute value of the various dimensions are desired (instead of relative data).
Currently the generally known types of optically based 3D imaging technologies are discussed briefly below:
Laser Triangulation: This approach uses a laser spot or a laser line to scan an object. A detector array in another angle receives the signal and calculates the triangulation angle related to the Z distance. It takes anywhere from a few seconds to minutes to take a 3D image of an object. This is too slow for taking 3D images of a live object, and the laser beam is potentially harmful to the eyes.
Structured Illumination: This approach projects a structured light pattern on an object, then analyzes the deformation of the reflected light pattern as imaged by a two dimension detector array to calculate the "Z" distance, or depth. It has the problem of matching each pattern in the reflected image with the illumination pattern. This can produce ambiguity in the results thus obtained. This is because the accuracy of the measurement is not high because a group of pixels, rather than a single pixel, is used to calculate the "Z" distance, again introducing ambiguity in the results.
Optical Moire and Interferometer: In order to resolve the ambiguity problem and to increase the accuracy of the measurement, such types of imaging systems rely upon measurement of the optical phase shift of reflected patterns of light to obtain and digitize the dimensional information of an object. It is necessary to move an optical grating, through which a pattern of light is projected unto the object, three to four times and to take three to four consecutive images in order to apply the mathematical formulae necessary to calculate the phase shift and extract the dimensional data from the reflected images.
Moire and Interferometer based systems are more accurate, but they are also expensive and difficult to use. In most cases, such systems also need to acquire multiple exposures, which makes them unsuitable for live object digitization. Attempts have been made to use three color gratings to perform a phase shift Moire operation. But such attempts have been unsuccessful because they could not improve the cross talk between the color bands present in the grating (and projected on the object).
Stereoscopic Imaging: This approach uses two cameras to map the 3D surface of an object. They require identification of common features in both images, such as edges and corners. Thus they can not extract Z distance information from a single pixel, but must also extrapolate this information from a group of pixels, resulting once again in inaccuracy. The matching of the features with the actual object also requires heavy computation.
Time-of-Flight Method: This approach relies upon a short pulsed laser beam that hits the surface of the object and by calculating the time delay of the light traveling from the laser transmitter to the object surface and back to a receiver. This method requires the scanning of a laser point on the object surface and so it is also slow. It also requires a very high speed laser transmitter-receiver, therefore it is expensive.
Accordingly there exists today a need for a three dimensional imaging system that relies upon optical technologies, which is suitable for use on live or moving objects, which is fast to use, and which is inexpensive to manufacture, and which does not require especially complex mathematical computations to determine the dimensions of an object.
Clearly, such an apparatus and method is useful and desirable.
2. Description of Prior Art
Three dimensional imaging systems and methods are, in general, known. For example, the following patents describe various types of these devices:
U.S. Pat. No. 3,589,815 to Hosterman, Jun. 29, 1971; PA1 U.S. Pat. No. 3,625,618 to Bickel, Dec. 7, 1971; PA1 U.S. Pat. No. 4,247,177 to Marks et al, Jan. 27, 1981; PA1 U.S. Pat. No. 4,299,491 to Thornton et al, Nov. 10, 1981; PA1 U.S. Pat. No. 4,375,921 to Morander, Mar. 8, 1983; PA1 U.S. Pat. No. 4,473,750 to Isoda et al, Sep. 25, 1984; PA1 U.S. Pat. No. 4,494,874 to DiMatteo et al, Jan. 22, 1985; PA1 U.S. Pat. No. 4,532,723 to Kellie et al, Aug. 6, 1985; PA1 U.S. Pat. No. 4,594,001 to DiMatteo et al, Jun. 10, 1986; PA1 U.S. Pat. No. 4,764,016 to Johansson, Aug. 16, 1988; PA1 U.S. Pat. No. 4,935,635 to O'Harra, Jun. 19, 1990; PA1 U.S. Pat. No. 4,979,815 to Tsikos, Dec. 25, 1990; PA1 U.S. Pat. No. 4,983,043 to Harding, Jan. 8, 1991; PA1 U.S. Pat. No. 5,189,493 to Harding, Feb. 23, 1993; PA1 U.S. Pat. No. 5,367,378 to Boehnlein et al, Nov. 22, 1994; PA1 U.S. Pat. No. 5,500,737 to Donaldson et al, Mar. 19, 1996; PA1 U.S. Pat. No. 5,568,263 to Hanna, Oct. 22, 1996; PA1 U.S. Pat. No. 5,646,733 to Bieman, Jul. 8, 1997; PA1 U.S. Pat. No. 5,661,667 to Bordignon et al, Aug. 26, 1997; and PA1 U.S. Pat. No. 5,675,407 to Geng, Oct. 7, 1997.
While the structural arrangements of the above described devices, at first appearance, have similarities with the present invention, they differ in material respects. These differences, which will be described in more detail hereinafter, are essential for the effective use of the invention and which admit of the advantages that are not available with the prior devices.